Membrane Structure Flashcards 1.3

Questions and Answers

Describe the structure of a phospholipid.

A phospholipid consists of a polar (hydrophilic) phosphate group head, a glycerol molecule, and 2 non-polar (hydrophobic) fatty acid tails.

Why do phospholipids form bilayers?

They form bilayers because the polar hydrophilic group heads project outwards to be attracted to water, while the non-polar hydrophobic fatty acid tails extend inwards away from water.

The main part of a phospholipid bilayer consists of the fatty acid tails which make the plasma membrane relatively permeable to polar molecules and ions.

True

Explain Gorter and Grendel's model.

Gorter and Grendel calculated that the area the phospholipids occupied when in a monolayer was twice as large as the area of the plasma membrane and deduced that it contained a bilayer. Signup and view all the answers

There was no explanation of where proteins are located in the membrane in Gorter and Grendel's model.

True Signup and view all the answers

Explain Singer and Nicholson's model.

Singer and Nicholson found that proteins occupy various positions in the membrane; integral proteins are embedded and sometimes protrude out, while peripheral proteins are attached to the surface. Signup and view all the answers

Explain Davson and Danielli's sandwich model.

Davson and Danielli proposed that there were layers of protein adjacent to the phospholipid bilayer on both sides of the plasma membrane, creating a sandwich appearance. Signup and view all the answers

What are the problems with the sandwich model?

The sandwich model didn't explain the presence and movement of proteins; evidence from freeze-etched electron microscopy and fluorescent tagging challenged its validity. Signup and view all the answers

What did the problems with the Davson-Danielli model lead to?

They led to the acceptance of Singer and Nicholson's fluid mosaic model. Signup and view all the answers

Describe the structure of plasma membranes.

Plasma membranes are phospholipid bilayers that are very narrow, typically 7-10nm in width. Signup and view all the answers

What is the function of plasma membranes at the surface of cells?

Plasma membranes control which molecules or ions enter or leave a cell, managing the exchange with the environment. Signup and view all the answers

Plasma membranes allow for cell-to-cell attachment which enables tissues to form.

True Signup and view all the answers

How do plasma membranes partake in cell recognition and communication?

They engage in cell recognition and communication via receptors and signaling molecules on their surfaces. Signup and view all the answers

What is the function of plasma membranes in eukaryotic cells?

Plasma membranes control the exchange between the cytoplasm and the external environment. Signup and view all the answers

Study Notes

Phospholipid Structure

Composed of a hydrophilic phosphate group head, a glycerol molecule, and two hydrophobic fatty acid tails.
Bilayer formation occurs due to the polar heads repelling water while the non-polar tails avoid it, creating an orientation ideal for cell environments.

Phospholipid Bilayer Characteristics

Fatty acid tails primarily constitute the bilayer, granting the membrane permeability to polar molecules and ions.

Gorter and Grendel's Model

Calculated area occupied by phospholipids in monolayer was double that of the plasma membrane, indicating a bilayer presence.
Their methods had flaws, yet these did not undermine the conclusion that membranes are phospholipid bilayers.

Limitations of Gorter and Grendel's Model

Failed to address the location of proteins within the membrane, highlighting a significant gap in understanding membrane structure.

Singer and Nicholson's Fluid Mosaic Model

Established that proteins are found in various configurations: peripheral proteins on the membrane surface and integral proteins embedded within.
Proteins appear as a mosaic due to their varied positions, with phospholipids permitting fluid movement, hence the term "fluid mosaic model."

Davson and Danielli's Sandwich Model

Proposed a model where protein layers were adjacent to the phospholipid bilayer, creating a sandwich effect to explain substance barriers.
High magnification electron microscopy revealed a distinct appearance supporting their model, with dark proteins and lighter phospholipids.

Critique of the Sandwich Model

Experimental evidence, such as freeze-etched microscopy, demonstrated transmembrane proteins, contradicting the fixed-layer concept.
Fluorescent antibody tagging showed intermixing of membrane proteins, indicating mobility rather than fixed positions.

Shift to the Fluid Mosaic Model

Evidence gathered against the Davson-Danielli model necessitated a new understanding, leading to widespread acceptance of the Singer-Nicholson model.

Structure of Plasma Membranes

Plasma membranes are phospholipid bilayers with a width of 7-10 nm, contributing to their thin and flexible nature.

Functions of Plasma Membranes

Regulate molecular and ionic exchange, acting as selective barriers to polar substances.
Facilitate cell attachment and tissue formation, enhancing structural organization within multicellular organisms.
Participate in cell recognition and communication, crucial for tissue functionality and immune response.

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Description

Explore the key concepts of membrane structure through these flashcards. Learn about phospholipid composition and the importance of bilayer formation in cellular environments. Perfect for students looking to deepen their understanding of cell membranes.